spongebob v2.js

const isRegularCharacter = char => {
    const code = char.charCodeAt(0);

    return (code > 64 && code < 91) || (code > 96 && code < 123);
};

const mock = (str) => {
    let count = 0;

    return str
        .split("")
        .map(char => {
            if (!isRegularCharacter(char)) {
                return char;
            }

            return count++ % 2 === 0 ? char.toUpperCase() : char.toLowerCase();
        })
        .join("");
};

process.stdout.end(mock(process.argv.slice(2).join(" ")));